1. Field of the Invention
The present invention relates to an accelerometer and an angular accelerometer suitable for, e.g., control of driving of an arm and the like of a robot when used as a displacement sensor.
2. Related Background Art
Conventionally, an accelerometer and an angular accelerometer have been used in various fields of, e.g., a seismometer, a vibrometer, and a shock meter, and control of driving of various arms of a robot.
Many conventional accelerometers (including angular accelerometers) sense displacement of a pendulum or a spring, caused by acceleration, by using a displacement sensor, thereby obtaining the acceleration. Examples of this displacement sensor are an eddy-current type sensor, an electric-capacitance type sensor, and a differential-transformer type sensor. The sensitivities of these displacement sensors are generally, readily influenced by an intense electromagnetic field and are also susceptible to changes in, e.g., temperature and pressure. On the other hand, an optical sensor, such as an encoder, is available as a displacement sensor not easily influenced by environmental changes.
FIG. 1 is a schematic view showing a main part of a displacement detection unit of an accelerometer proposed in Japanese Laid-Open Utility Model Application No. 61-87363.
Referring to FIG. 1, a thin plate-like member 73 having a slit 72 is provided at the end portion of a rod-like pendulum 71 which is displaced on the basis of an acceleration applied to it. A light-emitting unit 74 and a light-receiving unit 75 are arranged to sandwich the thin plate-like member 73 between them. The displacement of the pendulum 71 is obtained by detecting a light quantity balance between two light-receiving elements 75a and 75b constituting the light-receiving unit 75, thereby obtaining the applied acceleration.
FIG. 2 is a schematic view showing a main part of a displacement detection unit of an accelerometer proposed in Japanese Laid-Open Patent Application No. 2-249974.
Referring to FIG. 2, a movable member 83 is provided at one end of a support 82 fixed on a fixed member 81. A light beam from a light-emitting unit 85 is condensed by a condenser lens 84 held by the movable member 83 and is converged onto a light-receiving unit 86. The displacement of the support 82 which is displaced on the basis of an applied acceleration is obtained by detecting a light quantity balance between two light-receiving elements 86a and 86b constituting the light-receiving unit 86, thereby obtaining the applied acceleration.
FIG. 3 is a block diagram showing a main part of an angular accelerometer for controlling driving of an arm of a robot by using a conventional rotary encoder.
Referring to FIG. 3, a detection unit 93 detects an angular position signal from a motor 92 in accordance with a signal from an encoder 91. A first arithmetic unit 94 differentiates the signal from the detection unit 93 to obtain the velocity of the motor. A second arithmetic unit 95 differentiates the velocity signal from the first arithmetic unit 94 to obtain the angular acceleration of the motor 92.
In each of the accelerometers shown in FIGS. 1 and 2, since the signal detected by the light-receiving unit is a signal of an analog quantity, noise components in that signal, for example, cause complexity in arithmetic processing upon performing servo control. This also brings about a problem of difficulty in increasing the detection resolution and the detection sensitivity.
In addition, the light-emitting unit and the light-receiving unit are disposed to oppose each other with the light-transmitting movable member located between them. This arrangement requires a large space, and consequently the overall apparatus tends to increase in size.
The angular accelerometer shown in FIG. 3, on the other hand, requires a complicated circuit for allowing the arithmetic units to differentiate the angular signal obtained by the encoder. The result is a decrease in detection accuracy, and this makes it difficult to control driving of a motor with high accuracy.